In the United States, vast quantities of nitrogen are sent from homes and industries to centralized wastewater treatment plants. Much of the nitrogen passing through a modern wastewater treatment plant practicing Biological Nutrient Removal (BNR) is intentionally nitrified, then denitrified, and volatilized to be discharged into the atmosphere, mainly as dinitrogen (N2) gas with small amounts of N2O, to dispose of it. Moreover, much of the nitrogen is collected as solids and anaerobically digested into the form of ammonium only to be subsequently diluted into a larger flux for further treatment. Paradoxically, at the same time wastewater treatment plants are diluting, discharging and disposing of nitrogen, the fertilizer industry is, with great effort and expense, fixing atmospheric nitrogen with natural gas using the Haber-Bosch process for fertilizer production.
Anaerobic digestion of solid wastes has long been practiced in the wastewater industry as a method to reduce the amount and environmental impact of solids separated from wastewater and, more recently as an optimized process for generating energy, gaining broader application in animal feeding operations, dairies and food processing facilities. During anaerobic digestion, microorganisms convert organic matter into carbon dioxide and methane, which are gases. Soluble nutrient ions, among them ammonium, potassium, monohydrogen phosphate and dihydrogen phosphate, are concentrated in the anaerobic digest at levels much greater than the original wastewater. Nitrogen is prevented from oxidation from ammonium to nitrate by the prevailing anaerobic conditions of the digestion process.
Attempts have been made to recover nitrogen from raw wastewater via electrodialysis. Specifically, electrodialysis has been investigated as an approach for recovering ammonia from swine manure. For example, Mondor et al. (2008, 2009) used electrodialysis coupled with reverse osmosis for the recovery and concentration of ammonia, estimating a maximum total ammonium—N concentration of about 16 g/L could be reached. They found that over time a significant deposit, calcium carbonate and silica colloidal particles, formed on the ion-exchange membranes and the ion-exchange capacity could only be partially restored after cleaning, making long-term use of the electrodialysis system infeasible. Mondor, M., Masse, L., Ippersiel, D., Lamarche, F. and Masse, D. I., 2008, Use of electrodialysis and reverse osmosis for the recovery and concentration of ammonia from swine manure, Bioresource Technology 99, pg: 7363-7368; and Fouling characterization of electrodialysis membranes used for the recovery and concentration of ammonia from swine manure, M. Mondor, D. Ippersiel, F. Lamarche, L. Masse, Bioresource Technology 100 (2009) 566-571.